Sometimes the touchline must feel like the bleakest, loneliest place on earth. André Villas-Boas has endured numerous troubling moments in his brief spell so far in the Stamford Bridge hot-seat, but in the 20th minute of an FA Cup tie against Championship opposition he appeared to plummet to new depths of isolation.

In the context of a horrible week, which began with defeat at Everton and then saw reports of a heated team meeting crank up the pressure, there was no room for error. Yet Chelsea erred. Even though he tries very hard to show he is in control, to transmit an unflappable self-belief where everyone else sees turmoil, Villas-Boas's face could not help but betray his stress as chaotic defending from a set play allowed Birmingham to lash a goal past Petr Cech. Chelsea's young manager looked like he was trying not to flinch as the boos were vociferous enough to drown out the elation emanating from the visiting supporters.

Desperate times call for desperate measures, and Villas-Boas responded by hooking Fernando Torres at half-time after another colourless performance. On came Didier Drogba, with his cajoling words and rousing gestures – such different vibes to the downcast body language Torres transmits these days.

When Villas-Boas was quizzed afterwards about the misfiring Spaniard, he went into auto-pilot, trotting out the same old lines he has peddled all season. It is understandable, really. Anything other than offering a few complimentary words without really addressing this continuous problem would only make things worse.

Is it possible that the Torres conundrum is going to do for two successive Chelsea managers? Although on the surface it seems Carlo Ancelotti was ousted because he deigned to go one season without winning a trophy, there is no question that the friction over the use of one of Roman Abramovich's pet signings did not help the Italian's cause in the eyes of the club's owner. Torres's flaky form is a headache that Villas-Boas inherited and one he has not been able to cure.

This foible at Chelsea, where Abramovich occasionally appears to have certain players in which he invests more than just money, is a tricky one.

A similar thing happened with Andriy Shevchenko, a player whose arrival seemed to represent some sort of personal mission for the owner. The Ukrainian had been coveted by Abramovich for some time. Milan did not want to sell, but Chelsea's persistence, and £30.9m, pushed through a deal.

Yet his time in London seldom showcased Shevchenko at his most striking. Injuries were part of the problem, but the fact José Mourinho was reluctant to play him became a thorny issue behind the scenes. It is never the easiest scenario when players are bought for the owner's tastes instead of the coach's needs.

The Torres situation is even more pressured than Shevchenko for several reasons: the squad around him is poorer than it was during Shevchenko's era; the dreaded transfer fee, as a British record, remains a millstone; Torres is that much younger, which makes the suggestion that he might be a spent force that much more difficult to accept.

While it would be no surprise to see the remnants of Mourinho's "untouchables" – such as John Terry, Frank Lampard and Drogba – moving on in the not too distant future, at some point somebody has to make a decision about what to do with Torres. It is alarming to see such an experienced, top-class player still straining to play his way back into the groove more than a year after a big move.

It would be fascinating to get a really straight answer, rather than the autopilot, from Villas-Boas about exactly where Torres fits into "the Project". The Portuguese has not hidden from the fact this is a season of transition for Chelsea. But one of the fundamental things that has to be transformed along the way is Torres. So far, no good.

And so to Napoli. Drogba, the man to make Chelsea's day on countless occasions, will expect to be installed at the head of the team. Understandably, he may have been tired after his stint at the Africa Cup of Nations, but he still found it difficult to make a big impression during the second half against Birmingham in which Chelsea were marginally less lousy than they had been in the opening 45 minutes.

Some supporters chose a more subtle way to tell the hierarchy what they thought, by joining in with Birmingham fans who ironically chanted: "José Mourinho, José Mourinho." The shadow of the man who built a great team that is on its last legs still looms large.